Washable ink composition

ABSTRACT

The present invention concerns a washable aqueous ink composition comprising: a) at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, 5b) at least one salt of polyacrylic acid, c) at least one dye. It also concerns a writing instrument comprising it and the use of the association of a) at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon and b) at least one salt of polyacrylic acid, to improve the washability 10 and/or vividness of the shades of a washable aqueous ink composition

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of International Application No. PCT/EP2021/077285, filed on Oct. 4, 2021, now published as WO2022/073925A1 and which claims priority to European Application No. 20306159.3, filed on Oct. 6, 2020, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure concerns washable/rinsable ink compositions, more specifically aqueous washable ink compositions.

Existing washable ink compositions contain « conventional » dyes which are often acid dyes, soluble in water. These dyes can be Food dyestuffs or if not, these dyes must be in conformity with the Toy's Regulation in place if the products are dedicated to children.

The word “washable” means that stains may be removed from common washable fabrics after 1 to 3 washes at 40° C. following ISO 6330:2012 standard.

The “washable” inks contain generally glycol in order to manage surface tension of the inks and to limit the drying of the nib in case the cap of the marker or felt pen is off.

The dyes used have generally a “substantive” character, the size of the dye molecules is so small and the surface tension of the ink is usually low that the stains are difficult to remove from the substrate, mainly on the skin. There is a penetration of the dye molecules into the porosity of the surface.

Existing washable ink formulations having better washability requirements and more specifically whose stains may be removed from the skin with tepid water and soap, contains specific dyes which are often polymeric dyes. These dyes are not Food dyestuffs but these dyes must be in conformity with the Toy's Regulation in place if the products are dedicated to children.

These inks are usually much more expensive and the shades obtained with the polymeric dyes are generally less vivid than the ones obtained with conventional Acid dyes.

SUMMARY

The aim of the disclosure is to formulate washable inks having better washability requirements, more specifically being washable from the skin even with cold water, and containing “conventional dyes” such as acid dyes in order to have more vivid color.

More specifically the inventors have found that there was a synergy in the combined used of a salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms and a salt of polyacrylic acid.

Indeed this combination improves the skin washability of the ink, more specifically with water, even more specifically without using soap, evenl more specifically using cold water. Moreover acid dyes could be used with this combination in the washable ink, which provides vivid color to the ink.

DETAILED DESCRIPTION

The present disclosure therefore concerns a washable aqueous ink composition comprising:

a) at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, more specifically an alkali metal salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, and even more specifically wherein the alkali metal salt is sodium,

b) at least one salt of polyacrylic acid, specifically an alkali metal salt of polyacrylic acid, more specifically sodium polyacrylate,

c) at least one dye.

Hereinafter, a detailed description of the present disclosure will be given. The specific embodiments are meant to better illustrate the present disclosure, however, it should be understood that the present disclosure is not limited to these specific embodiments.

In the sense of the present disclosure, the expression “comprising a” should be understood as being synonymous with “comprising at least one”.

In the sense of the present disclosure, the expressions “between . . . and . . .” or “ranging from . . . to . . .” should be understood as including the values of the limits.

As indicated above, in the sense of the present disclosure, “a washable ink” is intended to mean any ink, the stains of which may be removed from common washable fabrics after 1 to 3 washes at 40° C. following ISO 6330 :2012 standard.

More specifically, the washable ink composition according to the present disclosure is a writing ink. For the purposes of the present disclosure, the term “writing ink” is intended to mean any ink which is intended to be used in a writing instrument, and more specifically in a felt-pen, a highlighter, a roller pen or a marker. A writing ink should not be confused with a printing ink which is used in printing machines and which does not have the same technical constraints, and thus the same specifications. Indeed, a writing ink must not contain solid particles of which the size is greater than the channels of the writing instrument, in order to avoid blocking them, which would inevitably lead to writing being irreversibly stopped. It must also dry sufficiently rapidly to avoid smudging the writing medium. It must also avoid the problems of migration (bleeding) over time. Thus, the writing ink composition according to the present disclosure will be suitable for the writing instrument for which it is intended, more specifically for handheld writing instrument, such as a felt-pen, a highlighter, a roller pen, or a marker. More specifically, the “washable ink” according to the disclosure is suitable on porous substrate.

For the purposes of the present disclosure, the term “porous substrate” is intended to mean substrate that contains pores. The porous substrates have empty spaces or pores that allow external matter, like ink, to penetrate into the substrate. More specifically, writing surfaces such as white board or enamel board are not considered as writing porous substrate. More specifically, the porous substrates are fibrous. For example, the “porous substrate” can be fabrics (such as flax, cotton) such as clothes, cellulosic fiber paper such as paper (printer paper for example) and cardboard paper.

The ink according to the present disclosure is an “aqueous ink”. The term “aqueous ink” is intended to mean in the context of the present disclosure a water-based ink, i.e. any ink which contains an aqueous solvent, more specifically water, as the main solvent. In an advantageous embodiment the total amount of the aqueous solvent, more specifically water, is ranging from 20 to 95 wt. %, and even more specifically from 30 to 90 wt. %, and even more specifically from 35 to 85 wt. %, still more specifically from 40 to 75 wt. %, based on the total weight of the washable aqueous ink composition.

The ink according to the present disclosure comprises at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms.

More specifically the salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms has the following formula (I):

R—(CO₂X)_(n)   (I)

in which R represents a C₂-C₇ alkyl group which can be substituted by one or several —OH group (more specifically 1 to 5 —OH group), n=1 to 4 and X is the counter-ion, even more specifically an alkali metal such as sodium or potassium, even more specifically sodium.

For the purposes of the present disclosure, the term “C₂-C₇ alkyl group” is intended to mean any linear or branched alkyl group having from 2 to 7 carbon atoms, more specifically the ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl group and the like, even more specifically the n-propyl or n-pentyl group.

More specifically the C₂-C₇ alkyl group is substituted by one or several —OH group (even more specifically 1 to 5 —OH group). More specifically the n-propyl group is substituted by one —OH group and the n-pentyl group is substituted by 5 —OH group.

More specifically the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is a salt of monocarboxylic acid (n=1) with from 3 to 8 carbon atoms such as the salt of gluconic acid, dicarboxylic acid (n=2) with from 3 to 8 carbon atoms or tricarboxylic acid (n=3) with from 3 to 8 carbon atoms, such as the salt of citric acid or mixture thereof, even more specifically a salt of dicarboxylic acid (n=2) with from 3 to 8 carbon atoms or tricarboxylic acid (n=3) with from 3 to 8 carbon atoms, or mixture thereof, even more specifically a salt of tricarboxylic acid (n=3) with from 3 to 8 carbon atoms such as a citrate salt.

More specifically the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is an alkali metal salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, more particularly a sodium or potassium salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, for example the alkali metal salt is sodium.

More specifically the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is selected in the group consisting of salts of gluconic acid, salts of citric acid and mixture thereof, even more specifically in the group consisting of alkali metal salts of gluconic acid, alkali metal salts of citric acid (which can be optionally hydrated) and mixture thereof, even more specifically in the group consisting of sodium citrate, sodium gluconate and mixture thereof; more particularly it is sodium citrate, even more specifically the trisodium citrate dihydrate.

More specifically the total amount of the at least one salt of monocarboxylic or polycarboxylic acid is ranging from 0.5 to 30 wt. %, and more specifically from 1 to 20 wt. %, and even more specifically from 2.5 to 17 wt. %, based on the total weight of the washable aqueous ink composition.

The ink according to the present disclosure also comprises at least one salt of polyacrylic acid, specifically an alkali metal salt of polyacrylic acid, more particularly sodium or potassium salt of polyacrylic acid, more specifically it is sodium polyacrylate. It is available commercially for example under the name Sokalan® PA 15, Sokalan® PA 20, Sokalan® PA 40 from BASF.

More specifically, the average molar mass (Mw) of at least one salt of polyacrylic acid is ranging from 500 g/mol to 300 000 g/mol, and more specifically from 800 g/mol to 120 000 g/mol, and more specifically from 1100 g/mol to 17 000 g/mol. The average molar mass is determined by gel permeation chromatography (GPC) with aqueous eluents. The columns were calibrated with samples of sodium polyacrylates with a very wide molar mass distribution. Their molar masses are measured by a combined GPC/laser-light-scattering method, calculating the area under the curve. The calibration method described by M. J. R. Cantow (J. Polym. Sci. A-1, 5 (1967), 1391-1394) is used, but the concentration correction recommended by Cantow is not employed.

More specifically the total amount of the at least one salt of polyacrylic acid is ranging from 0.2 to 15 wt. %, and even more specifically from 0.5 to 10 wt. %, and more specifically from 1 to 8 wt. %, based on the total weight of the washable aqueous ink composition.

More specifically, the washable aqueous ink composition of the disclosure comprises a weight ratio of at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms/one salt of polyacrylic acid ranging from 0.1:1 to 100:1, even more specifically in a weight ratio from 0.5:1 to 50:1, more specifically 0.5:1 to 10:1.

The ink composition of the disclosure also comprises at least one dye, more specifically a mixture of dyes, solubilized in water. The term “dyes” should be understood as meaning colored, mineral or organic particles of any form, which are soluble in the medium in which they are solubilized (here water), and which are intended to color the ink composition. The at least one dye may be selected in the group consisting of direct dyes (for example C.I direct black 17, 19, 22, 32, 38, 51, 71; C.I direct yellow 4, 26, 44, 50; C.I direct red 1, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, 227; C.I direct blue 1, 15, 41, 71, 86, 87, 106, 108, 199, and the like), acid dyes (for example C.I acid black 1, 2, 24, 26, 31, 52, 107, 109, 110, 119, 154; C.I acid yellow 1, 7, 17, 19, 23, 25, 29, 38, 42, 49, 61, 72, 78, 110, 127, 135, 141, 142; C.I acid red 8, 9, 14, 18, 26, 27, 33, 35, 37, 51, 52, 57, 82, 83, 87, 92, 94, 111, 129, 131, 138, 186, 249, 254, 265, 276; C.I acid violet 15, 17, 49; C.I acid blue 1, 3, 7, 9, 15, 22, 23, 25, 40, 41, 43, 62, 78, 83, 90, 93, 100, 103, 104, 112, 113, 158; C.I acid green 3, 9, 16, 25, 27; C.I acid orange 56, and the like), food dyes (such as C.I. food yellow 3, and the like), Malachite green (C.I 4200) Victoria blue FB (C.I. 44045) methyl violet FN (C.I. 42535), rhodamine F4G (C.I. 45160), and rhodamine 6GCP (C.I 45160), and mixtures thereof. More specifically, the at least one dye comprises an acid dye, even more specifically it consists in an acid dye.

More specifically the total amount of the at least one dye is ranging from 0.01 to 20 wt. %, and even more specifically from 0.01 to 15 wt. %, and more specifically from 0.1 to 10 wt. %, still more specifically from 1 to 6 wt. %, based on the total weight of the washable aqueous ink composition.

The ink composition of the disclosure can further contains at least one humectant, the at least one humectant being more specifically a water-soluble alcohol having a melting point of less than 20° C. and a boiling point of at least 150° C., even more specifically the at least one humectant has a solubility in water of at least 10 g/L at 20° C., even more specifically at least 20 g/L at 20° C. The humectant lets to improve the « cap-off », i.e. the ability of the ink composition of not drying up in the writing instrument, which means more specifically that the writing instrument can be left open for longer period of time, more specifically one hour or even several hours, even more specifically with removed cap-off, without drying up. More precisely, the humectant comprises an aliphatic alcohol wherein the hydrocarbon chain can be interrupted or not by one or more heteroatom, more specifically chosen from oxygen, nitrogen and sulfur, even more specifically oxygen and even more specifically wherein the alcohol has at least 2 hydroxyl groups. The humectant is more specifically selected in the group consisting of glycerin, ethylene glycol, sorbitol, diethylene glycol, triethylene glycol, propylene glycol, and thiodiglycol, and mixtures thereof, even more specifically in the group consisting of glycerin, sorbitol and mixtures thereof, more particularly it is sorbitol, even more specifically D-sorbitol. It is or example available on the market in the name Neosorb® 70/70 from Roquette.

More specifically the total amount of the at least one humectant is ranging from 1 to 50 wt. %, and even more specifically from 2 to 40 wt. %, and more specifically from 5 to 35 wt. %, based on the total weight of the washable aqueous ink composition.

The ink composition according to disclosure can further contain an additive known by the skilled person to be usable in aqueous ink compositions, more specifically in aqueous writing ink compositions, even more specifically selected in the group consisting of antimicrobial agents, antifungal agents, dispersing agents, wetting agents, pH regulators, rheology modifiers and mixtures thereof.

More specifically the total amount of the additive is ranging from 0.05 to 15 wt. %, and even more specifically from 0.075 to 10 wt. %, based on the total weight of the washable aqueous ink composition.

More specifically among the additives, the ink composition of the disclosure may even more specifically contain at least one antimicrobial agent such as methyl paraben, phenoxyethanol, isothiazolinone, 1,2-benzoisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and mixtures thereof.

More specifically, the antimicrobial agent is present in the ink composition of the disclosure in a content ranging from 0.05 to 5% by weight, and even more specifically from 0.075 to 2% by weight, based on the total weight of the washable aqueous ink composition.

More specifically among the additives, the ink composition of the present disclosure may also contain a pH regulator, even more specifically chosen in the group consisting of ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of phosphoric acid such as tripolyphosphate, sodium carbonate and hydroxides of alkali metals such as sodium hydroxide.

The present disclosure also concerns a method for preparing a washable aqueous ink composition according to the disclosure, comprising the steps of:

-   -   (i) under stirring, adding the optional additive(s) and the at         least one dye to water,     -   (ii) under stirring, adding the optional humectant and the at         least one salt of monocarboxylic or polycarboxylic acid with         from 3 to 8 carbon atoms to the mixture obtained in step (i) and     -   (iii) under stirring, adding the at least one salt of         polyacrylic acid.

The at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, at least one salt of polyacrylic acid, at least one dye, water, as well as the optional humectant and additive(s), are as defined above for the washable aqueous ink composition according to the disclosure.

During steps (i), (ii) and (iii), the ink ingredients are mixed under stirring more specifically at a temperature of between 40 and 50° C., even more specifically at a temperature of 45° C.+/−2° C., even more specifically at a stirring speed ranging from 200 to 700 rpm, and even still more specifically at a stirring speed of 500 rpm.

The ink composition obtained in steps (i), (ii) and (iii), can be homogenized during a certain period of time ranging from 15 to 50 minutes, and more specifically from 25 to 45 minutes.

The present disclosure also concerns a writing instrument, more specifically a handheld writing instrument, more specifically a pen such as a felt-pen, a highlighter, a roller pen or a marker, and more even more specifically it is a writing felt-pen, a coloring felt-pen, a highlighter, containing an ink composition according to the disclosure.

According to a preferred embodiment, the writing instrument according to the present disclosure comprises:

-   -   an axial barrel containing an ink composition according to the         disclosure, and     -   a pen body which delivers the ink composition stored in the         axial barrel.

The present disclosure finally concerns the use of the association of a) at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon and b) at least one salt of polyacrylic acid, more specifically as described above, to improve the washability (even more specifically on skin and clothes) and/or vividness of the shades of a washable aqueous ink composition. More specifically the use is for improving the washability of a washable aqueous ink composition, particularly the water washability of a washable aqueous ink composition, more particular the water washability without soap, more particularly when washing with cold water.

In addition to the foregoing, the disclosure also comprises other provisions which will emerge from the additional description which follows, which relates to the preparation of writing ink compositions according to the present disclosure and comparative examples.

Example 1: Preparation of Ink Compositions According to the Present Invention and Comparative Ink Compositions

Compositions according to the invention (Ex 1 and Ex 2) and comparative compositions (without any salt of polyacrylic acid: comparative Ex 1 or without any salt of monocarboxylic or polycarboxylic acid: comparative Ex 2) were prepared. Their ingredients and weight % are indicated in table 1.

TABLE 1 ingredients, function and % by weight of the ink composition Ex 1 in Ex 2 in Comparative Comparative Chemical name wt. % wt. % Ex 1 in wt. % Ex 2 in wt. % Function Water 55.50 55.50 70.50 60.50 Solvent Trisodium citrate 15.00 5.00 5.00 washable dihydrate additive (sodium citrate) Sokalan PA 15 15.00 15.00 15.00 washable (polyacrylic acid, (i.e. 6.75% (i.e. 6.75% (i.e. 6.75% additive sodium salt) of pure of pure of pure (45 wt. % polyacrylic polyacrylic polyacrylic polyacrylic acid, acid, sodium acid, sodium acid, sodium sodium salt in salt) salt) salt) water) Neosorb 70/70 10.00 20.00 20.00 20.00 Cap-off (sorbitol syrup) additive Acid blue 9 1.60 1.60 1.60 1.60 Dye Acid red 18 1.20 1.20 1.20 1.20 Dye Acid red 52 0.80 0.80 0.80 0.80 Dye Acid yellow 23 0.80 0.80 0.80 0.80 Dye Methylparaben 0.10 0.10 0.10 0.10 Biocide Total 100.0% 100.0% 100.0% 100.0%

The process of preparation of these ink compositions are as follow:

Comparative Ex 1: For a preparation of 1 kg, 705 g of deionized water were introduced and heated at 45° C.+/−2° C. (maintain the temperature until the end of the manufacturing) in a dissolver DISPERMAT® LC75 (dissolver disc ∅60 mm), and 1 g of Methylparaben were added under agitation (stirring speed: 500 rpm). After 5 min, the dyes were added successively at the same stirring speed; 16 g of Acid Blue 9, 12 g of Acid Red 18, 8 g of Acid red 52 and 8 g of Acid Yellow 23. After 15 minutes, 200 g of Neosorb 70/70 were introduced and also 50 g of sodium citrate. The mixture was stirred for 15 minutes more to obtain the final ink composition.

Comparative Ex 2: For a preparation of 1 kg, 605 g of deionized water were introduced and heated at 45° C.+/−2° C. (maintain the temperature until the end of the manufacturing) in a dissolver DISPERMAT® LC75 (dissolver disc ∅60 mm), and 1 g of Methylparaben were added under agitation (stirring speed: 500 rpm). After 5 min, the dyes were added successively at the same stirring speed; 16 g of Acid Blue 9, 12 g of Acid Red 18, 8 g of Acid red 52 and 8 g of Acid Yellow 23. After 15 minutes, 200 g of Neosorb 70/70 were introduced and also 150 g of Sokalan PA15. The mixture was stirred for 10 minutes more to obtain the final ink composition.

EX 1: For a preparation of 1 kg, 555 g of deionized water were introduced and heated at 45° C.+/−2° C. (maintain the temperature until the end of the manufacturing) in a dissolver DISPERMAT® LC75 (dissolver disc ∅60 mm), and 1 g of Methylparaben were added under agitation (stirring speed: 500 rpm). After 5 min, the dyes were added successively at the same stirring speed ; 16 g of Acid Blue 9, 12 g of Acid Red 18, 8 g of Acid red 52 and 8 g of Acid Yellow 23. After 15 minutes, 100 g of Neosorb 70/70 were introduced and also 150 g of sodium citrate. After 15 min, 150 g of Sokalan PA15 were added and the mixture was stirred for 10 minutes more to obtain the final ink composition.

EX 2: For a preparation of 1 kg, 555 g of deionized water were introduced and heated at 45° C.+/−2° C. (maintain the temperature until the end of the manufacturing) in a dissolver DISPERMAT® LC75 (dissolver disc ∅60 mm), and 1 g of Methylparaben were added under agitation (stirring speed: 500 rpm).

After 5 min, the dyes were added successively at the same stirring speed ; 16 g of Acid Blue 9, 12 g of Acid Red 18, 8 g of Acid red 52 and 8 g of Acid Yellow 23. After 15 minutes, 200 g of Neosorb 70/70 were introduced and also 50 g of sodium citrate. After 15 min, 150 g of Sokalan PA15 were added and the mixture was stirred for 10 minutes more to obtain the final ink composition.

Example 2: Washability Tests of the Ink Compositions According to the Present Invention and Comparative Ink Compositions

The following tests were performed on the ink compositions (Ex 1, Ex 2, comparative Ex 1 and comparative Ex 2).

Washability Performance: Measurement of Skin Washability with Cold Water and without Soap

This test is the ability of the consumer to wash correctly the written mark applied on the skin with cold water and without soap.

The method is as follows:

-   -   1. Clean hands before performing this test.     -   2. Make a smear (dimension 2×1 cm) to back of the hand.     -   3. Allow to dry for 15 min (do not wash the hands during this         drying time).     -   4. After 15 min of drying, place the hand under cold water         (10-15°) during 15 seconds, without rubbing hands.     -   5. Dry the hands with absorbent paper and evaluate the scoring         of this test.

The scoring of this test is defined as follows:

-   -   10: The washability of the ink composition is very efficient.     -   7.5: The washability of the ink composition is efficient (with         very slight remaining traces).     -   5: The washability of the ink composition is not very efficient         (with visible remaining traces).     -   2.5: The washability of the ink composition is not efficient         (traces hardly removed).     -   0: The washability of the ink composition is not efficient at         all (traces not removed).

The results are indicated in Table 2 below.

Washability Performance: Measurement of Skin Washability with Tepid Water (30-35° C.) and Soap

This test is the ability of the consumer to wash correctly the written mark applied on the skin with tepid water (30-35° C.) and soap.

The method is as follows:

-   -   1. Clean hands before performing this test.     -   2. Make a smear (dimension 2×1 cm) to back of the hand.     -   3. Allow to dry for 1 hour (do not wash the hands during this         drying time).     -   4. After 1 hour of drying, place the hand under tepid water         (30-35°) during 15 seconds, and add soap (for example Marseille®         soap) while rubbing hands during 10 to 15 seconds.     -   5. Rinse the hands under tepid water (30-35° C.).     -   6. Dry the hands with absorbent paper and evaluate the scoring         of this test.

The scoring of this test is defined as follows:

-   -   10: The washability of the ink composition is very efficient.     -   7.5: The washability of the ink composition is efficient (with         very slight remaining traces).     -   5: The washability of the ink composition is not very efficient         (with visible remaining traces).     -   2.5: The washability of the ink composition is not efficient         (traces hardly removed).     -   0: The washability of the ink composition is not efficient at         all (traces not removed).

The results are indicated in Table 2 below.

Washability Performance: Measurement of Cloth Washability Resistance (Line Method)

This test is the ability of the consumer to wash correctly the written mark applied by line method on fabrics.

Equipment

-   -   1. Air conditioned and humidity controlled room: 23° C. (±2°);         50% RH (±5% RH).     -   2. Washing machine according to ISO 6330:2012 type A standard         (such as Programmable Wascator Fom71 CLS Electrolux Lab washing         machine)     -   3. Detergent:         -   77 g of European Colorfastness Establishment detergent basis         -   20 g of tetrahydrated sodium perborate         -   3 g of tetra-acetyl-ethylene diamine     -   4. Diacetate-Wool multifibers (DW) fabric strip for staining         with the following materials: wool, polyacrylic, polyester,         polyamide, cotton, acetate (ISO 105 F10 standard)     -   5. 2 kg of additional load fabric (type II, 50% cotton, 50%         polyester (ISO 6330:2012 standard))

The method is as follows:

-   -   1. Fix the fabric strip on a non-porous support thanks to pins         in order to keep the fabric flat and properly laid.     -   2. Draw three lines about 10 cm length on fabric strip.     -   3. Let the fabric strip on air dry in room with conditioned air         during 24 hours.     -   4. Put the fabric strip in the washing machine drum and add the         corresponding additional load fabric: 50% cotton, 50% polyester.     -   5. Put 20 g of detergent in the tank dedicated to powder.     -   6. Launch the washing program (40° C.).     -   7. When washing is finished, take out both the fabric strip and         loads from the machine and let them air dry during 24 hours         minimum.     -   8. Evaluate the scoring of this test.     -   9. If written mark is visible after 1^(st) washing, repeat steps         6, 7, 8 of this method.

The scoring of this test is defined as follows:

-   -   10/10: The washability of the ink composition is very efficient.     -   7.5/10: The washability of the ink composition is efficient         (with very slight remaining traces).     -   5/10: The washability of the ink composition is not very         efficient (with visible remaining traces).     -   2.5/10: The washability of the ink composition is not efficient         (traces hardly removed).     -   0/10: The washability of the ink composition is not efficient at         all (traces not removed).

The results are indicated in Table 2 below.

Washability Performance: Measurement of Cloth Washability Resistance (Capillarity Method)

This test is the ability of the consumer to wash correctly the written mark by capillary method applied on fabrics.

Equipment

-   -   1. Air conditioned and humidity controlled room: 23° C. (±2°);         50% RH (±5% RH).     -   2. Washing machine according to ISO 6330:2012 type A standard         (such as Programmable Wascator Fom71 CLS Electrolux Lab washing         machine)     -   3. Detergent:         -   77 g of European Colorfastness Establishment detergent basis         -   20 g of tetrahydrated sodium perborate         -   3 g of tetra-acetyl-ethylene diamine         -   4. Diacetate-Wool multifibers (DW) fabric strip for staining             with the following materials: wool, polyacrylic, polyester,             polyamide, cotton, acetate (ISO 105 F10 standard)         -   5. 2 kg of additional load fabric (type II, 50% cotton, 50%             polyester (ISO 6330:2012 standard))

The method is as follows:

-   -   1. Fix the fabric strip on a non-porous support thanks to pins         in order to keep the fabric flat and properly laid.     -   2. Transfer ink drop from the pen tip during 5 seconds on fabric         strip     -   3. Let the fabric strips on air dry in room with conditioned air         during 24 hours.     -   4. Put the fabric strip in the washing machine drum and add the         corresponding additional load fabric: 50% cotton, 50% polyester.     -   5. Put 20 g of detergent in the tank dedicated to powder.     -   6. Launch the washing program (40° C.).     -   7. When washing is finished, take out both the fabric strip and         loads from the machine and let them air dry during 24 hours         minimum.     -   8. Evaluate the scoring of this test.     -   9. If written mark is visible after 1^(st) washing, repeat steps         6, 7, 8 of this method.

The scoring of the test is defined as follows:

-   -   10/10: The washability of the ink composition is very efficient.     -   7.5/10: The washability of the ink composition is efficient         (with very slight remaining traces).     -   5/10: The washability of the ink composition is not very         efficient (with visible remaining traces).     -   2.5/10: The washability of the ink composition is not efficient         (traces hardly removed).     -   0: The washability of the ink composition is not efficient at         all (traces not removed).

The results are presented in table 2 below

TABLE 2 results of the tests Test Ex 1 Ex 2 Comp Ex 1 Comp Ex 2 Skin washability cold User 1 7.5 7.5 5 5 water without soap 15s User 2 7.5 7.5 2.5 5 Skin washability tepid User 1 10 10 10 10 water with soap 15s User 2 10 10 7.5 10 Cloth washability Wool 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) resistance wash wash wash wash LINE METHOD Polyacrylic 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Polyester 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Polyamide 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Cotton 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Acetate 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Cloth washability Wool 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) resistance wash wash wash wash CAPILLARITY Polyacrylic 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) METHOD wash wash wash wash Polyester 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Polyamide 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Cotton 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash Acetate 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) 10/10 1^(st) wash wash wash wash

As can be seen, the ink compositions according to the invention (Ex 1 and Ex 2) exhibit good results in terms of washability. Indeed, the compositions have good washability on clothes of different materials and on skin, with tepid water and with cold water as well, even without soap. In particular, the washability of the ink compositions according to the invention (Ex 1 and Ex 2) exhibit better results in terms of skin washability and in particular with cold water, when compared to the ink composition without any salt of monocarboxylic or polycarboxylic acid (Comparative Ex 2) and when compared to ink composition without any salt of polyacrylic acid (Comparative Ex 1). 

1. A washable aqueous ink composition comprising: a) at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms, b) at least one salt of polyacrylic acid, c) at least one dye.
 2. The washable aqueous ink composition according to claim 1, wherein the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is a salt of monocarboxylic acid with from 3 to 8 carbon atoms, dicarboxylic acid with from 3 to 8 carbon atoms or tricarboxylic acid with from 3 to 8 carbon atoms or mixture thereof.
 3. The washable aqueous ink composition according to claim 1, wherein the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is selected in the group consisting of salts of gluconic acid, salts of citric acid and mixture thereof. 4-15. (canceled)
 16. The washable aqueous ink composition according to claim 1, wherein the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is selected in the group consisting of sodium citrate, sodium gluconate and mixture thereof.
 17. The washable aqueous ink composition according to claim 1, wherein the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is an alkali metal salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms.
 18. The washable aqueous ink composition according to claim 1, wherein the total amount of the at least one salt of monocarboxylic or polycarboxylic acid with from 3 to 8 carbon atoms is ranging from 0.5 to 30 wt. %, based on the total weight of the washable aqueous ink composition.
 19. The washable aqueous ink composition according to claim 1, wherein the at least one salt of polyacrylic acid is an alkali metal salt of polyacrylic acid.
 20. The washable aqueous ink composition according to claim 1, wherein the at least one salt of polyacrylic acid is sodium polyacrylate.
 21. The washable aqueous ink composition according to claim 1, wherein the total amount of the at least one salt of polyacrylic acid is ranging from 0.2 to 15 wt. %, based on the total weight of the washable aqueous ink composition.
 22. The washable aqueous ink composition according to claim 1, wherein the at least one dye comprises an acid dye.
 23. The washable aqueous ink composition according to claim 1, wherein the total amount of the at least one dye is ranging from 0.01 to 20 wt. %, based on the total weight of the washable aqueous ink composition.
 24. The washable aqueous ink composition according to claim 1, wherein it further contains at least one humectant.
 25. The washable aqueous ink composition according to claim 24, wherein the at least one humectant is a water-soluble alcohol having a melting point of less than 20° C. and a boiling point of at least 150° C.
 26. The washable aqueous ink composition according to claim 24, wherein the at least one humectant has a solubility in water of at least 10 g/L at 20° C.
 27. The washable aqueous ink composition according to claim 22, wherein the at least one humectant is selected in the group consisting of glycerin, ethylene glycol, sorbitol, diethylene glycol, triethylene glycol, propylene glycol, thiodiglycol, and mixtures thereof.
 28. The washable aqueous ink composition according to claim 24, wherein the total amount of the at least one humectant is ranging from 1 to 50 wt. %, based on the total weight of the washable aqueous ink composition.
 29. The washable aqueous ink composition according to claim 1, wherein it contains an additive.
 30. The washable aqueous ink composition according to claim 26, wherein the total amount of additive is ranging from 0.05 to 15 wt. % based on the total weight of the washable aqueous ink composition.
 31. The washable aqueous ink composition according to claim 1, wherein the total amount of water is ranging from 20 to 95 wt. %, based on the total weight of the washable aqueous ink composition.
 32. A writing instrument comprising a washable aqueous ink composition as claimed in claim
 1. 